U.S. patent application number 11/220710 was filed with the patent office on 2007-03-08 for gas mixture for removing photoresist and post etch residue from low-k dielectric material and method of use thereof.
Invention is credited to Robert Charatan, Tom Choi, Alan Jensen, Cristian Paduraru, David Schaefer.
Application Number | 20070054496 11/220710 |
Document ID | / |
Family ID | 37830547 |
Filed Date | 2007-03-08 |
United States Patent
Application |
20070054496 |
Kind Code |
A1 |
Paduraru; Cristian ; et
al. |
March 8, 2007 |
Gas mixture for removing photoresist and post etch residue from
low-k dielectric material and method of use thereof
Abstract
Atomic oxygen generated in oxygen stripping plasmas reacts with
and damages low-k dielectric materials during stripping of
dielectric post etch residues. While damage of low-k dielectric
materials during stripping of dielectric post etch residues is
lower with hydrogen stripping plasmas, hydrogen stripping plasmas
exhibit lower strip rates. Inclusion of oxygen in a hydrogen
stripping plasma improves both photoresist strip rate and
uniformity, while maintaining a hydrogen to oxygen ratio avoids
low-k dielectric material damage.
Inventors: |
Paduraru; Cristian;
(Fremont, CA) ; Jensen; Alan; (White Salmon,
WA) ; Schaefer; David; (Vancouver, WA) ;
Charatan; Robert; (Portland, OR) ; Choi; Tom;
(San Jose, CA) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
37830547 |
Appl. No.: |
11/220710 |
Filed: |
September 8, 2005 |
Current U.S.
Class: |
438/725 ;
134/1.1; 216/67 |
Current CPC
Class: |
G03F 7/427 20130101 |
Class at
Publication: |
438/725 ;
216/067; 134/001.1 |
International
Class: |
B08B 6/00 20060101
B08B006/00; H01L 21/461 20060101 H01L021/461; H01L 21/302 20060101
H01L021/302; B44C 1/22 20060101 B44C001/22 |
Claims
1. A method of removing photoresist and post etch residue from a
semiconductor substrate having a layer of low-k dielectric material
comprising: introducing a semiconductor substrate having a layer of
low-k dielectric material having photoresist and post etch residue
thereon into a downstream reaction chamber; generating plasma
comprising reactive species in an upstream applicator, wherein the
reactive species comprise atomic hydrogen and atomic oxygen,
wherein atomic oxygen passivates applicator surfaces exposed to the
plasma, wherein the plasma is generated from a gas mixture
comprising oxygen, hydrogen, and inert carrier gas, and wherein the
volume ratio of hydrogen to oxygen is greater than 2:1; and
introducing the reactive species into the downstream reaction
chamber, wherein atomic hydrogen removes photoresist and post etch
residue from the low-k dielectric material.
2. The method of claim 1, wherein the gas mixture comprises
0.05-0.3% by volume oxygen and 1-10% by volume hydrogen.
3. The method of claim 2, wherein the gas mixture comprises about
0.1% by volume oxygen.
4. The method of claim 3, wherein the reactive species introduced
into the downstream reaction chamber comprise less than about 0.1%
by volume oxygen.
5. The method of claim 1, wherein the inert carrier gas is selected
from the group consisting of helium, argon, and mixtures
thereof.
6. The method of claim 5, wherein the inert carrier gas is helium
and further wherein hydrogen and helium are supplied as
H.sub.2He.
7. The method of claim 1, wherein the oxygen is supplied as
O.sub.2.
8. The method of claim 1, wherein the gas mixture has a total flow
rate of up to about 6000-7000 standard cubic centimeters per
minute.
9. The method of claim 1, wherein the semiconductor substrate is a
semiconductor wafer supported on a substrate support heated to a
temperature of at least 250.degree. C.
10. The method of claim 1, wherein the volume ratio of hydrogen to
oxygen is greater than 5:1, greater than 10:1, greater than 20:1,
or greater than 40:1.
11. The method of claim 1, wherein the reactive species are
introduced into the downstream reaction chamber through a quartz
baffle and further wherein atomic oxygen passivates baffle surfaces
exposed to the plasma.
12. The method of claim 1, wherein the reactive species are exposed
to a quartz chamber liner before being introduced into the
downstream reaction chamber and further wherein atomic oxygen
passivates chamber liner surfaces exposed to the plasma.
13. The method of claim 1, wherein the upstream applicator is
comprised of quartz.
14. The method of claim 1, further comprising seasoning the
reaction chamber with an oxygen-containing gas, which is energized
into a plasma state for a time sufficient to remove polymer
byproducts deposited on chamber surfaces, prior to introducing the
semiconductor substrate into the downstream reaction chamber.
15. A method of sequentially processing semiconductor wafers
comprising: a) removing photoresist and post etch residue from a
semiconductor substrate according to the method of claim 14; b)
removing the semiconductor wafer from the downstream reaction
chamber; and c) repeating steps a) and b).
16. A gas mixture for removing photoresist and post etch residue
from a semiconductor substrate having a layer of low-k dielectric
material comprising: hydrogen and oxygen in a volume ratio of
greater than 2:1; and inert carrier gas, wherein plasma generated
from the gas mixture comprises atomic hydrogen and atomic oxygen,
wherein atomic oxygen passivates surfaces exposed to the plasma,
and wherein atomic hydrogen removes photoresist and post etch
residue from the low-k dielectric material.
17. The gas mixture of claim 16, comprising: 0.05-0.3% by volume
oxygen; and 1-10% by volume hydrogen.
18. The gas mixture of claim 17, comprising about 0.1% by volume
oxygen.
19. The gas mixture of claim 16, wherein the inert carrier gas is
helium, the hydrogen and helium are supplied as H.sub.2He, and the
oxygen is supplied as O.sub.2.
20. The gas mixture of claim 16, wherein the volume ratio of
hydrogen to oxygen is greater than 5:1, greater than 10:1, greater
than 20:1, or greater than 40:1.
Description
BACKGROUND
[0001] During a standard dielectric etch processing sequence, a
semiconductor substrate having a dielectric layer is masked with a
sacrificial masking layer such as photoresist and hard mask, the
dielectric in those areas not protected by the mask is etched, and
then the residue remaining from the mask and caused by the etch
process, such as residue from photoresist, is removed.
SUMMARY
[0002] Provided is a method of removing photoresist and post etch
residue from a semiconductor substrate having a layer of low-k
dielectric material comprising introducing a semiconductor
substrate having a layer of low-k dielectric material having
photoresist and post etch residue thereon into a downstream
reaction chamber and generating plasma comprising reactive species
in an upstream applicator. The reactive species comprise atomic
hydrogen and atomic oxygen, atomic oxygen passivates applicator
surfaces exposed to the plasma, the plasma is generated from a gas
mixture comprising oxygen, hydrogen, and inert carrier gas, and the
volume ratio of hydrogen to oxygen is greater than 2:1. The
reactive species are introduced into the downstream reaction
chamber and atomic hydrogen removes photoresist and post etch
residue from the low-k dielectric material.
[0003] Also provided is a gas mixture for removing photoresist and
post etch residue from a semiconductor substrate having a layer of
low-k dielectric material comprising hydrogen and oxygen in a
volume ratio of greater than 2:1 and inert carrier gas. Plasma
generated from the gas mixture comprises atomic hydrogen and atomic
oxygen, atomic oxygen passivates surfaces exposed to the plasma,
and atomic hydrogen removes photoresist and post etch residue from
the low-k dielectric material.
BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS
[0004] FIG. 1 shows a microwave reaction chamber having, inter
alia, an applicator in which plasma containing reactive species is
generated, a baffle through which reactive species are introduced
into the reaction chamber, and a chamber liner which is exposed to
the reactive species before the reactive species are introduced
into the reaction chamber.
[0005] FIG. 2 depicts an embodiment of a resist stripping chamber
including a baffle, FIG. 3 illustrates an embodiment of a baffle,
and FIG. 4 illustrates a liner positioned on the baffle shown in
FIG. 3.
[0006] FIG. 5 shows the intensity of hydrogen as a function of
oxygen flow in plasma formed from helium, hydrogen, and oxygen in
the apparatus of FIG. 1.
[0007] FIGS. 6 and 7 show the intensity of hydrogen as a function
of time in plasma formed from helium and hydrogen and plasma formed
from helium, hydrogen, and oxygen, in the apparatus of FIG. 1.
[0008] FIG. 8 shows Scanning Electron Microscopy (SEM) results of
residue removal from a low-k dielectric material. FIG. 8a shows SEM
results of residue removal from a low-k dielectric material using
6240 standard cubic centimeters per minute (sccm) He and 260 sccm
H.sub.2. FIG. 8b shows SEM results of residue removal from a low-k
dielectric material using 6240 sccm He, 260 sccm H.sub.2, and 5
sccm O.sub.2. FIG. 8c shows SEM results of residue removal from a
low-k dielectric material using 6240 sccm He, 260 sccm H.sub.2, and
20 sccm O.sub.2.
[0009] FIG. 9 shows photoresist strip rates minus photoresist
shrinkage and uniformity for residue removal from a low-k
dielectric material using 6240 sccm He, 260 sccm H.sub.2, and 0
sccm O.sub.2, 5 sccm O.sub.2, or 20 sccm O.sub.2.
DETAILED DESCRIPTION
[0010] Oxygen stripping plasmas are beneficial for stripping
dielectric post etch residues when the dielectric is a form of
SiO.sub.2, as oxygen stripping plasmas remove the residue at high
rates and do not damage the dielectric. On the other hand, the use
of an oxygen stripping plasma is not beneficial for stripping
dielectric post etch residues when the dielectric is a low-k
dielectric material, as such materials usually contain carbon, and
atomic oxygen in the plasma would react with the carbon, thereby
damaging the low-k dielectric material.
[0011] "Low-k dielectric" materials are defined herein as materials
with a dielectric constant k that is less than 3. Low-k materials
include, but are specifically not limited to, benzocyclobutene or
BCB; Flare.TM. manufactured by Allied Signal.RTM. of Morristown,
N.J., a division of Honeywell, Inc., Minneapolis, Minn.; one or
more of the Parylene dimers available from Union Carbide.RTM.
Corporation, Danbury, Conn.; polytetrafluoroethylene or PTFE; and
SiLK.RTM.. One interesting class of organic low-k materials is
compounds including organosilicate glass, or OSG. By way of
example, but not limitation, such organosilicate dielectrics
include CORAL.TM. from Novellus of San Jose, Calif.; Black
Diamond.TM. from Applied Materials of Santa Clara, Calif.; Sumika
Film.RTM. available from Sumitomo Chemical America, Inc., Santa
Clara, Calif., HOSP.TM. from Allied Signal of Morristown, N.J, and
LKD products from JSR Micro of Sunnyvale, Calif. Organosilicate
glass materials have carbon and hydrogen atoms incorporated into
the silicon dioxide lattice which lowers the dielectric constant of
the material.
[0012] Hydrogen stripping plasmas may also be used for stripping
dielectric post etch residues. While damage of low-k dielectric
materials is minimal with hydrogen stripping plasmas as compared to
oxygen stripping plasmas, hydrogen stripping plasmas exhibit lower
strip rates than oxygen stripping plasmas.
[0013] The use of a remote plasma source, for example, a preferred
upstream microwave reactor, does not introduce energetic ions to
the semiconductor substrate, but does introduce atomic hydrogen to
the semiconductor substrate, and as a consequence, is also
beneficial for reducing low-k dielectric material damage. Remote
plasma sources are described in commonly owned U.S. Pat. Nos.
6,080,270, 6,388,383, 6,692,649, and 6,777,173, incorporated herein
by reference in their entirety. Referring to the upstream microwave
reactor of FIG. 1, plasma including reactive species such as atomic
hydrogen may be generated in an applicator upstream of the reaction
chamber and the reactive species introduced into the downstream
reaction chamber. While the reaction chamber may be maintained at
750 mTorr-1 Torr, the pressure in the applicator may be about 6
Torr. The microwave reaction chamber may also comprise a chamber
liner, which is exposed to reactive species during the stripping
operation.
[0014] It has been discovered that inclusion of oxygen in a
hydrogen stripping plasma improves both photoresist strip rate and
uniformity and that by maintaining a hydrogen to oxygen ratio low-k
dielectric material damage can be avoided. It is believed that
atomic oxygen passivates reaction chamber surfaces exposed to the
reactive species, such as, for example, the applicator, a baffle,
or a chamber liner, so as to reduce recombination of atomic
hydrogen on the exposed surfaces.
[0015] Thus, oxygen indirectly enhances photoresist strip rate by
increasing the relative amount of atomic hydrogen available for the
strip process by substantially reducing the probability of atomic
hydrogen recombination on such exposed surfaces. It is believed
that as oxygen passivates the exposed surfaces, there are fewer
sites with which atomic hydrogen may react and therefore, the
amount of atomic hydrogen distributed in the reaction chamber is
increased. It is believed that as oxygen passivates the exposed
surfaces, there are fewer sites that atomic oxygen may passivate,
and eventually, saturation occurs. Thus, at higher percentages of
oxygen, atomic oxygen will directly react with and damage the low-k
dielectric material. As the recombination rate of hydrogen on
quartz is lower the recombination rate of hydrogen on other
materials, reaction chamber surfaces exposed to the reactive
species, such as, for example, the applicator, a baffle, or a
chamber liner, are preferably comprised of quartz.
[0016] The reactive species may be distributed into the reaction
chamber through a baffle having surfaces exposed to the reactive
species, and atomic oxygen may passivate the surfaces of the baffle
exposed to the reactive species, thereby reducing recombination of
atomic hydrogen at the surfaces of the baffle exposed to the
reactive species. Atomic oxygen may passivate the surface of a
chamber liner before being introduced into the reaction chamber,
thereby reducing the probability of atomic hydrogen recombination
at the chamber liner surface.
[0017] FIG. 2 depicts an exemplary embodiment of a resist stripping
chamber 10 in which a baffle 50 is mounted. The resist stripping
chamber 10 includes a side wall 12, a bottom wall 14 and a cover
16. The cover 16 is preferably pivotably attached by hinges to the
side wall 12 to allow the cover 16 to be opened to access the
interior of the resist stripping chamber 10 to remove the baffle 50
for cleaning or replacement, or for other purposes. The resist
stripping chamber 10 includes vacuum ports 18 in the bottom wall
14.
[0018] The resist stripping chamber 10 also includes a substrate
support 20 on which a semiconductor substrate 22, such as a wafer,
is mounted during resist stripping. The substrate support 20
preferably comprises an electrostatic chuck adapted to clamp the
substrate 22. The substrate support 20 preferably includes a
heater, such as a resistive heating element, adapted to maintain
the substrate 22 at a suitable temperature during the resist
stripping process. The substrate 22 can be introduced into and
removed from the resist stripping chamber 10 through a substrate
entry port 26 provided in the sidewall 12. For example, the
substrate 22 can be transferred under vacuum into the interior of
the resist stripping chamber 10 from an etching chamber located
proximate the resist stripping chamber.
[0019] A remote plasma source 30 is arranged in fluid communication
with the resist stripping chamber 10. The plasma source 30 is
operable to produce plasma and to supply reactive species into the
interior of the resist stripping chamber 10 through a passage 32
connected to the resist stripping chamber 10. The illustrated
embodiment of the plasma source 30 includes a remote energy source
34 and a stripping gas source 36. The energy source 34 can be any
suitable source and is preferably a microwave generator. Exemplary
apparatuses including a microwave generator are available from Lam
Research Corporation, Freemont, Calif. In a preferred embodiment,
the microwave generator operates at a frequency of 2.45 GHz, and
preferably has a power in the range of about 500 to about 3000 W,
more preferably in the range of about 1000 to about 1500 W.
Microwaves, represented by arrow 38, are produced by the microwave
generator 34 and propagated through a waveguide 40 into the passage
32.
[0020] The gas source 36 is operable to supply process gas,
represented by arrow 42, into the passage 32, or applicator, where
the gas is energized into the plasma state by the microwaves
produced by the energy source 34. Reactive species pass through an
opening 44 into the interior of the resist stripping chamber
10.
[0021] The reactive species are distributed in the resist stripping
chamber 10 by a baffle 50 located between the cover 16 and the
substrate support 20 before the reactive species flow onto the
substrate 22 and strip the resist. The substrate 22 is preferably
heated by a heater located in the substrate support 20 during
resist stripping. Waste products generated during resist stripping
are pumped out of the resist stripping chamber 10 through the
exhaust ports 18.
[0022] As shown in FIG. 3, the baffle 50 may be a circular,
one-piece body. The resist stripping chamber 10 is preferably
cylindrical for single wafer processing. When adapted to be
installed in a cylindrical resist stripping chamber 10, the baffle
50 preferably has a diameter larger than the width, e.g., diameter,
of the interior of the resist stripping chamber 10 so that the
baffle can be supported by the side wall 12. The baffle 50 includes
an inner portion having a raised central portion 52 with an upper
surface 54 and through passages 56. In the illustrated embodiment
of the baffle 50, the central portion 52 includes six
circumferentially spaced-apart passages 56. The number of passages
56 can be either more or less than six in other embodiments. In the
embodiment, ultraviolet (UV) radiation that passes through the
passage 32 impinges on the upper surface 54 in a direction
generally perpendicular to the upper surface. The passages 56 are
preferably oriented at an acute angle relative to the upper surface
54 to prevent a direct line of sight for the UV radiation to pass
through the baffle 50. Consequently, the UV radiation is reflected
from the upper surface 54 and the walls of the passages 56 so that
it does not damage the substrate 22.
[0023] The baffle 50 also includes through passages 58 arranged
between the central portion 52 and a peripheral portion 60. The
passages 58 are adapted to distribute reactive species in a desired
flow pattern into the interior of the resist stripping chamber 10.
As shown in FIG. 3, the passages 58 preferably are in the form of
concentrically-arranged rows of holes. The passages 58 preferably
have a round cross section and preferably increase in
cross-sectional size (e.g., diameter) in the radial outward
direction of the baffle 50 from the central portion 52 toward the
peripheral portion 60.
[0024] As shown in FIG. 3, the peripheral portion 60 of the baffle
50 includes a flange 62 having circumferentially spaced-apart holes
64 for receiving fasteners 66, e.g., threaded bolts (FIG. 2), to
attach the baffle 50 to the top surface 68 of the side wall 12 of
the resist stripping chamber 10. The baffle 50 can be detached from
the side wall 12 and removed from the resist stripping chamber 10
to treat or replace the baffle, as desired.
[0025] As shown in FIG. 4, a liner 70 may be adapted to be
supported on the upper surface 72 of the baffle 50 to minimize the
deposition of materials on the bottom surface of the cover 16
during resist stripping processes. Circumferentially spaced-apart
spacers 65 are provided on the upper surface 72 to support the
liner 70 and form a plenum 74 therebetween (FIG. 2). The liner 70
includes a centrally located passage 44 through which reactive
species pass from the passage 32 into the plenum 74.
[0026] Provided is a method of removing photoresist and post etch
residue from a semiconductor substrate having a layer of low-k
dielectric material comprising introducing a semiconductor
substrate having a layer of low-k dielectric material having
photoresist and post etch residue thereon into a downstream
reaction chamber and generating plasma comprising reactive species,
such as atomic oxygen and atomic hydrogen, in an upstream
applicator. Atomic oxygen passivates applicator surfaces exposed to
the plasma. The plasma is generated from a gas mixture comprising
oxygen, hydrogen, and inert carrier gas, with a volume ratio of
hydrogen to oxygen of greater than 2:1, preferably greater than
5:1, more preferably greater than 10:1, even more preferably
greater than 20:1, and even more preferably greater than 40:1. The
plasma is preferably generated from a gas mixture comprising
0.05-0.3% by volume oxygen, more preferably about 0.1% by volume
oxygen, and 1-10% by volume hydrogen. The inert carrier gas may
comprise a noble gas, such as, for example, helium, argon, or
mixtures thereof. Hydrogen and helium may be supplied as H.sub.2He
and the oxygen may be supplied as O.sub.2. The gas mixture
preferably has a total flow rate of up to about 6000-7000 sccm,
more preferably up to about 6500 sccm. The reactive species are
introduced into the downstream reaction chamber and atomic hydrogen
removes photoresist and post etch residue from the low-k dielectric
material.
[0027] As it is believed that atomic oxygen passivates surfaces
exposed to the reactive species, such as, for example, the surface
of the applicator, for a plasma generated from a gas mixture
comprising about 0.1% by volume oxygen, 1-10% by volume hydrogen,
and inert carrier gas, the reactive species introduced into the
reaction chamber that are present at the semiconductor substrate
surface comprise less than about 0.1% by volume oxygen. The gas
mixture from which the plasma is formed is preferably free of
fluorocarbons, hydrofluorocarbons, ammonia, and N.sub.2H.sub.2.
Accordingly, the gas mixture preferably consists essentially of
oxygen, hydrogen, and inert carrier gas. The inert carrier gas may
comprise a noble gas, such as, for example, helium, argon, or
mixtures thereof. Hydrogen and helium may be supplied as H.sub.2He
and the oxygen may be supplied as O.sub.2.
[0028] The incorporation of oxygen in the hydrogen stripping gas is
beneficial in sequential processing of semiconductor wafers in that
a highly repeatable stripping process can be achieved from wafer to
wafer. Preferably, the reaction chamber is seasoned prior to
stripping the photoresist from each wafer. Accordingly, the
reaction chamber is seasoned prior to introducing a substrate into
the reaction chamber. The seasoning may comprise processing a bare
silicon wafer or Waferless Autoclean.TM.. The seasoning gas is
energized into a plasma state for a time sufficient to remove
polymer byproducts deposited on chamber surfaces during the
preceding stripping process. The seasoning gas is preferably an
oxygen-containing gas, such as, for example, a He:H.sub.2:O.sub.2
gas mixture or preferably O.sub.2N.sub.2. It is believed that
seasoning with an oxygen-containing gas passivates exposed surfaces
of the reaction chamber with oxygen. Thus, a method of sequentially
processing semiconductor wafers comprises removing photoresist and
post etch residue from a semiconductor substrate as described
above, removing the semiconductor wafer from the reaction chamber,
and repeating.
[0029] As disclosed above, additionally provided is a gas mixture
for removing photoresist and post etch residue from a semiconductor
substrate having a layer of low-k dielectric material comprising
hydrogen and oxygen in a volume ratio of greater than 2:1,
preferably greater than 5:1, more preferably greater than 10:1,
even more preferably greater than 20:1, and even more preferably
greater than 40:1, and inert carrier gas. Plasma generated from the
gas mixture comprises atomic hydrogen and atomic oxygen, wherein
atomic oxygen passivates surfaces exposed to the plasma, and
wherein atomic hydrogen removes photoresist and post etch residue
from the low-k dielectric material. The gas mixture preferably
comprises 0.05-0.3% by volume oxygen, more preferably about 0.1% by
volume oxygen, and 1-10% by volume hydrogen. The inert carrier gas
may comprise a noble gas, such as, for example, helium, argon, or
mixtures thereof. Hydrogen and helium may be supplied as H.sub.2He
and the oxygen may be supplied as O.sub.2.
[0030] As referred to herein, the intensity of hydrogen or oxygen
was measured by recording the emission intensity of the 656.3 nm
line of atomic hydrogen or the 777 nm line of atomic oxygen,
respectively, by Optical Emission Spectroscopy in the upstream
applicator of a microwave reactor, in which plasma was generated,
prior to the reactive species being introduced into a downstream
reaction chamber. The recorded emission intensity is proportional
to the concentration of species in the plasma, but dependent upon
such factor as, for example, electron temperature and collision
cross sectional area.
[0031] FIG. 5 shows the intensity of hydrogen as a function of
oxygen flow in plasma formed from helium, hydrogen, and oxygen.
Flow rates of 2850 sccm He and 150 sccm H.sub.2 (5% by volume) were
used. The intensity of hydrogen is observed to increase from 0 sccm
O.sub.2 to 5 sccm O.sub.2 (0.17% by volume). Greater than 5 sccm of
oxygen did not further significantly increase the intensity of
hydrogen.
[0032] FIGS. 6 and 7 show the intensity of hydrogen as a function
of time in plasma formed from helium and hydrogen and plasma formed
from helium, hydrogen, and oxygen. In the process illustrated by
FIG. 6, in which the power was 2600 W, the plasma formed from 2820
sccm He, 180 sccm H.sub.2, and 5 sccm O.sub.2 (0.17% by volume)
exhibited a greater intensity of hydrogen than did the plasma
formed from 2820 sccm He and 180 sccm H.sub.2 (6% by volume).
[0033] In the process illustrated by FIG. 7, the intensity of
hydrogen recorded in plasma generated from 6240 sccm He, 260 sccm
H.sub.2, and 6 sccm O.sub.2 (0.09% by volume) is greater than the
intensity of hydrogen recorded in plasma generated from 6240 sccm
He and 260 sccm H.sub.2 (4% by volume). Furthermore, for plasma
generated from 6240 sccm He and 260 sccm H.sub.2, the recorded
intensity of hydrogen decays to a saturation level, suggesting the
loss of atomic hydrogen during the process. It is believed that the
dominant mechanism of atomic hydrogen loss is atomic hydrogen
recombination at reaction chamber surfaces. Conversely, for plasma
generated from 6240 sccm He, 260 sccm H.sub.2, and 6 sccm O.sub.2,
the recorded intensity of hydrogen increases to a saturation level,
suggesting higher atomic hydrogen concentration in the plasma and
reduced atomic hydrogen recombination loss. It is believed that
atomic oxygen generated from inclusion of 6 sccm O.sub.2 passivates
reaction chamber surfaces, blocking available sites for atomic
hydrogen recombination and reducing the probability of atomic
hydrogen recombination, and thus, a higher concentration of atomic
hydrogen is available for reaction at the wafer surface.
[0034] In the process illustrated by FIG. 7, the power was 3000 W,
the chamber pressure was 750 mTorr, and the substrate temperature
was 280.degree. C. Substrate temperatures of greater than
250.degree. C. are preferred. Accordingly, the substrate,
preferably a semiconductor wafer, may be supported on a substrate
support heated to a temperature of at least 250.degree. C. The
substrate can be supported on a high temperature substrate support
with or without clamping of the substrate. Electrostatic chucks
suitable for use at high temperatures are disclosed in commonly
owned U.S. Pat. Nos. 6,377,437, 6,567,258, 6,669,783, incorporated
herein by reference in their entirety. If an electrostatic chuck is
used, it is not necessary to activate the electrostatic clamping
feature of the chuck.
EXAMPLES
[0035] FIG. 8 shows SEM results of residue removal from a low-k
dielectric material at a power of 3000 W (after treatment with
hydrofluoric acid for 30 seconds). FIG. 8a shows SEM results of
residue removal from a low-k dielectric material using 6240 sccm He
and 260 sccm H.sub.2 (4% by volume). FIG. 8b shows SEM results of
residue removal from a low-k dielectric material using 6240 sccm
He, 260 sccm H.sub.2, and 5 sccm O.sub.2 (0.08% by volume). FIG. 8c
shows SEM results of residue removal from a low-k dielectric
material using 6240 sccm He, 260 sccm H.sub.2, and 20 sccm O.sub.2
(0.31% by volume O.sub.2).
[0036] FIG. 9 shows photoresist strip rates minus photoresist
shrinkage and uniformity for residue removal from a low-k
dielectric material using 6240 sccm He, 260 sccm H.sub.2, and 0
sccm O.sub.2, 5 sccm O.sub.2, or 20 sccm O.sub.2.
[0037] As can be seen from FIGS. 8 and 9, residue removal from a
low-k dielectric material, photoresist strip rate (photoresist
strip rate minus photoresist shrinkage), and non-uniformity
(shrinkage subtracted) are all improved using 6240 sccm He, 260
sccm H.sub.2, and 5 sccm O.sub.2 (total flow rate of 6505 sccm) as
compared to 6240 sccm He, 260 sccm H.sub.2, and 0 sccm O.sub.2,
preferably without low-k dielectric material damage. The
photoresist shrinkage taken into account in calculating the
photoresist strip rate and non-uniformity occurs as a result of
using a heated electrode. As can further be seen from FIGS. 8 and
9, while 6240 sccm He, 260 sccm H.sub.2, and 20 sccm O.sub.2
exhibits better photoresist strip rate and non-uniformity, 6240
sccm He, 260 sccm H.sub.2, and 20 sccm O.sub.2 exhibits extensive
low-k dielectric material damage.
[0038] While various embodiments have been described, it is to be
understood that variations and modifications may be resorted to as
will be apparent to those skilled in the art. Such variations and
modifications are to be considered within the purview and scope of
the claims appended hereto.
* * * * *